KEYWORDS: Scanning electron microscopy, 3D image processing, 3D metrology, Design rules, Critical dimension metrology, Monte Carlo methods, Metrology, Manufacturing
As the manufacturing process is more integrated, in the field of metrology, there is an increasing demand for method to monitor local dispersion of measurement value that can trace randomly generated week points in the chip. Since it is difficult to obtain local dispersion with an optical method where the relatively large spot compared to the size of the target structure, many attempts have been made to use other method such as scanning electron microscopy (SEM). It is clear that SEM is suitable for obtaining local dispersion thanks to its high resolution, but it is difficult to obtain thickness information because only contrast data is included in the image. From these demands, a method using gray level (GL) index of the SEM image to estimate the depth of the target pattern has been proposed. However, because it is an index that simply correlates the GL value to the depth without considering pattern geometry, it follows different trends depending on the design rule and dispersion of the critical dimension (CD) and depth. In order to overcome this inhomogeneity of the GL index, in this study, we propose 3D GL index considering the field of view (FOV) of secondary electron (SE) emission according to the 3D geometry of the pattern. We apply effective FOV derived from SE emission function estimated by Lambertian distribution and CD and depth of the pattern to conventional GL index. As a result of applying it to the polysilicon hole pattern and comparing it with the vertical-SEM depth measurement, unlike the existing index, 3D GL index shows a clear linear trend with high correlation R2 of 0.781 regardless of design rule and dimension variation. In that it can more accurately and robustly respond to process variation, the proposed 3D GL index can increase the utilization of the depth monitoring method using SEM image.
As design rule of device shrinks quickly, process controls of HAR (high aspect ratio) buried defect become very crucial. In the past, monitoring of this defect mostly depended on e-beam inspection and destructive inspection. These methods cost a lot and need more time to prepare. So, optical inspection has been requested continuously. However, there are several technical obstacles, such as severe noises from under layers and quantification of defect height. In this study, we developed novel depth quantification technique for HAR structure. By using this new technique, we drastically improved (x240% higher) sensitivity of not-open defect. Light budget was rigorously analyzed and optimized for best SNR. To design deliberate non-destructive height quantification technique, we are currently working on development of TSOM (Through-focus Scanning Optical Microscopy) technique for HAR defect.
The evolution of 3D NAND memory devices is increasing the depth of HAR (High Aspect Ratio) hole structure. Consequently the technology to measure the shape of the structure is also becoming more difficult. In general, optical measurement method such as OCD (Optical Critical Dimension) is mainly used for measurement of the HAR structure, but optic technology has limitation in measurement of hole structure independently. To overcome this, SEM (Scanning Electron Microscopy) with high acceleration voltage of electron beam can be used for the measurement of bottom CD (Critical Dimension, diameter of a hole) of the hole structure. However this technology also has challenge in that the measured CD does not always represent the exact bottom CD of the structure. In order to solve this problem, we propose a method of inferring the actual depth where the measured CD is located by examining the change of the acceleration voltage and the angle of incident electron beam. The CDs of real product hole pattern were measured according to the change of landing energy of electron beam and the measured depth was calculated using proposed method. After inferring the CD measured from the actual hole structure, the method is verified in a sample having known structure figures. The proposed method can be used for 3D microstructure measurements using SEM technology in the future.
As the measurability (sampling capacity, measurement coverage, and measurement speed) of metrology systems are being enhanced to keep pace with the evolution of semiconductor manufacturing processes, the detection of defective areas and hidden weak patterns by analyzing the massive measurement data is becoming significantly important. In this study, we propose new methods to detect defective areas and hidden weak patterns by mathematically processing massive measurement data. By applying the methods we propose, we were able to successfully detect the hidden weak signals of the millimeter scale in the wafer.
In semiconductor industry, depth measurement is usually performed using the optical critical dimension (OCD) metrology, the atomic force microscopy (AFM) and transmission electron microscope (TEM). However, there are some limits in the depth measurements using OCD metrology or AFM. Therefore, this paper presents a new monitoring method for local depth using scanning electron microscopy (SEM) and a feasible verification method using AFM. This paper considers monitoring of local hole depth for the direct contact (DC). First, this paper proposes a depth monitoring index based on gray level (GL) of SEM image. The index includes not only the GL of the hole but also the GL of the background to reduce the effect of the GL inconsistency. Second, this paper verifies the effectiveness of the proposed depth monitoring index using in-FAB AFM. The reliability of the in-FAB AFM measurements as the reference for local depth is verified by TEM.
KEYWORDS: Semiconductors, Inspection, Data processing, Semiconductor manufacturing, Scanning electron microscopy, New and emerging technologies, High volume manufacturing
Historically, the development of high-density ICs has been a series of challenges, and we have overcame them and finally succeeded in mass production. However, the time from initiating product development to mass production is increasing, and moreover, it is taking longer than ever to reach maximum production yields. In this manufacturing environment, reducing development and yield ramping-up time is the most important factor in maximizing productivity and profit, and the key solution for this is MI technology. However, in order to respond to next-generation semiconductor products based on complex 3D structures, MI technology is going beyond the requirements especially for highly localized and non-destructive monitoring of 3D profiles. In this paper, we will discuss the evolutionary direction of these MI solutions. First, we will define the MI challenges that come along with the structural difficulties of new product, and review the changes in technology that have evolved in each field to overcome them. We will also explore the limitations of these technologies and see what new methodologies can be nominated to overcome them. We'll also look at what technical elements are required for HVM and what lessons can be learned from the examples in real production. Finally, we will propose how semiconductor MI technology should change its role through new innovations.
As the development technology of 3D NAND advances, it becomes increasingly important to measure the mid and bottom profiles of High-Aspect Ratio(HAR) hole or line structures. To estimate the HAR structure profile, SEM is generally used to measure the bottom CD using a high acceleration voltage, but there are cases where the measured CD does not represent actual bottom CD of the structure. To solve this problem, we propose a method of inferring the actual depth at which the measured CD is located by examining the CD change according to the change in the accelerating voltage of the electron beam and the inclination of the incident beam. After inferring the CD measured from the actual hole and line structure, the method was validated on samples with geometrically known structures. It is expected that the method approached in this paper can be used for 3D microstructure measurement using SEM technology in the future.
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